(CNN) -- New Kids on the Block singer Jonathan Knight left fans confused and concerned Thursday when he walked off stage in the middle of a concert in New York.According to reports, the five-member boy band was performing a mix of their old hits from the late '80s and early '90s, along with music from their new album, "10," when onlookers noticed that Knight seemed out of place.

HollywoodLife.com's Emily Longeretta was in the front row, and wrote on the celebrity website that Knight "seemed out of it. While the men started their choreographed dances, Jonathan stood uncomfortably in the background -- actually just standing and texting on his phone during the performance."